1. Field of the Invention
This invention relates to a diesel lubricant composition. More especially, the invention relates to silver corrosion inhibitors for diesel lubricant compositions. More particularly, the invention relates to a diesel lubricant composition with improved ability to protect the silver plated areas of a railway diesel engine such as the piston pin insert bearing-carrier combination.
2. Discussion of Prior Disclosures
Lubricant compositions of the type considered here are described in coassigned U.S. Pat. Nos. 4,169,799 and 4,172,269, the disclosures of which are incorporated herein by reference for their showing of railway diesel engine lubricant constitutents.
To elaborate on the background of the present invention, it has been found that railway diesel engine oils having a high degree of alkalinity, that is a TBN of at least 6, are particularly desirable in that they prevent corrosion by oil-soluble acids formed by oxidative deterioration at the high temperature existing under normal conditions of engine employment in proximity to the combustion chamber. The term "TBN" or nominal "TBN" as employed herein refers to "total base number" defined as the quantity of acid, expressed in terms of the equivalent number of milligrams of potassium hydroxide that is required to neutralize all basic constituents present in one gram of a given sample. The method of evaluation is described in ASTM Method D 664. While the foregoing alkalinity can be attained by introduction into the lube oil of a nominal 300 TBN forty percent to fifty percent overbased calcium sulfonate in a naphthenic oil carrier, the resulting lubricant compositions are unsatisfactory because these overbased materials degrade the silver protection characteristics of the oil, a factor of particular significance with respect to railway diesel engines, the vast majority of which, in the United States, and to a significant extent outside of the United States, as well, utilize silverplated piston pin insert bearings.
As described in the above-mentioned patents, particularly useful lubricant compositions are those containing substantially normal and/or highly overbased sulfurized calcium alklyphenolate and highly overbased alkaline earth metal sulfonate additives having a TBN of at least 10 and thus capable of preventing corrosion by oil-soluble acids formed by oxidative deterioration at the high temperatures existing under normal conditions of engine use in proximity to the combustion chamber. Where a sulfurized naphthenic oil-containing composition (having a sulfur content by weight of at least 1 percent) is incorporated with the foregoing overbased additives, the destruction of the silver protective properties of the lubricant oil by the overbased calcium alkylphenolate is overcome, but not the similarly destructive properties of the alkaline earth metal sulfonate. Nevertheless, the incorporation of an alkaline earth metal sulfonate in these lubricant oils is most desirable because of the improved engine performance it provides over an extended period of time.
Thus, the production of a finished lubricant oil for use in railway diesel engines having the necessary degree of alkalinity and, for this purpose, incorporating a normal or highly overbased sulfurized calcium alkylphenolate and an alkaline earth metal sulfonate, without dimunution of the silver protective properties of the finished lubricant oil would provide a significant advance in the state of the art.
In accordance with this invention there is provided a diesel lubricating oil composition comprising a diesel lubricating oil containing a silver corrosion inhibiting amount of at least one N-alkylaminomethyl-5-amino-1H-tetrazole.
The composition of the present invention contains the above additive in an amount from about 0.5 to 2.0 weight percent, preferably between 0.5 and 1 weight percent and especially at least 1 percent by weight.
The preparation of the reaction product used in a diesel lubricating composition according to the invention is relatively uncomplicated and can be economically conducted. An N-alkyl-1,3-propanediamine wherein the alkyl group has from 12 to 18 carbon atoms, formaldehyde and 5-amino tetrazole are reacted in substantially equimolar amounts to form the desired products.
The reaction is facilitated by the use of a solvent for the reactants which is inert to the reactants and to the reaction product. A broad range of inert organic, aromatic and aliphatic solvents are suitable for this purpose including xylene and methanol; preferably a mixture of xylene and methanol is used.
The reaction is broadly conducted at a temperature in the range of room temperature to about 150.degree. C., preferably 50.degree. to 100.degree. C. In practice, it is convenient to conduct the reaction at the reflux temperature of the solvent or solvent mixture employed for the reaction.
Suitable N-alkyl-1,3 propanediamines are those available commercially under the name of Duomeens (a product of Armak Co.) wherein the alkyl group is straight chain with an average of 12 to 18 carbon atoms and is attached to the nitrogen through the second carbon in the chain. Examples of suitable N-alkyl-1,3-propanediamine include N-oleyl-1,3-propane diamine (Duomeen O), N-stearoyl-1,3-propanediamine and N-tallow-1,3-propanediamine (Duomeen T).
The reaction product is believed to have the formula: ##STR1## wherein R is a straight chain alkyl having 12 to 18 carbon atoms as above set forth.
In the preparation of the corrosion inhibitor, 5-amino tetrazole, formaldehyde and the diamine are condensed at a temperature ranging from room temperature to about 150.degree. C. until a substantial completion of the reaction. The reaction is conducted in the absence of any catalyst, but generally in the presence of a solvent or diluent or mixture thereof to facilitate the reaction. The solvents or diluents are compatible with the components of the diesel crankcase lubricating oil.